RU2707689C2 - Apparatus and method for extracting metals and/or metal oxides from industrial wastes, particularly refinery wastes - Google Patents

Abstract

FIELD: heating, roasting, melting and retort furnaces.

SUBSTANCE: invention relates to extraction of metals from oil refining wastes. Extraction plant comprises a conveyor furnace, a supply pipeline, an outlet line, a leaching unit and one or more metal separation units. Supply pipeline is connected to the main inlet hole of the furnace for supply of the furnace with solid wastes containing metals, in particular, in oxide form. Output line is connected to the outlet hole of the solid phase furnace for extraction of the solid phase enriched with metal from the furnace. Conveyor furnace comprises an inner chamber extending along a substantially horizontal longitudinal axis and a closed belt conveyor in the chamber, having a substantially horizontal configuration along said axis, and also has an upper surface receiving the treated wastes and transmitting said wastes along said axis in the chamber between two longitudinally opposite ends of the conveyor furnace, having respectively a main inlet and an outlet for the solid phase. Leaching unit is installed after the conveyor furnace and is connected to the outlet hole for the solid phase of the conveyor furnace for the leaching of the solid phase leaving the conveyor furnace, and producing an aqueous solution containing metals extracted from said solid phase. Metal separation units are located after the leaching unit for at least partial separation of metals contained in the solution leaving the leaching unit.

EFFECT: simplified and cheaper leaching process.

26 cl, 6 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a plant and method for extracting metals and / or metal oxides from industrial wastes, in particular wastes from petroleum refining industries (refinery wastes).

BACKGROUND

Various industrial processes produce wastes containing metals (usually, but not exclusively, in the form of oxides).

For example, various wastes from petroleum refining processes contain metals and metal oxides, in particular such as: ash obtained in gasification processes; ash obtained in the processes of burning petroleum coke and / or heavy waste oil refining; purge emissions of hydroconversion by-product purification processes using suspension technology, such as processes with the names: EST suspension technology (ENI); VRSH technique (Chevron-Lummus-Global); HDH and HDHPLUS techniques (Intevep); SRC-Unifex methodology (UOP), (HC) 3 methodology (Headwaters).

Refinery waste usually contains high concentrations of valuable heavy metals such as Ni, V, Mo, usually in the form of oxides. These metals are widely used in the metallurgical industry and in the production of catalysts and, given the continuous increase in their price, their extraction can be interesting and economically viable.

The methods currently available for the extraction of these metals (Ni, V, Mo) from their oxides, essentially based on leaching methods, require that the carbon content does not exceed 5%, but oil refinery wastes, in particular those resulting from the above processes (gasification, burning petroleum coke and heavy oil refinery waste, hydroconversion purification processes using suspension technology) have a high carbon content in the form of coke and hydrocarbons. Therefore, pre-treatment is required to remove carbon (as well as moisture and hydrocarbons), usually performed through waste incinerators, namely:

a) multi-hearth furnaces (MHF),

b) rotary kilns,

c) fluidized bed combustion plants (FBC).

These systems have several drawbacks, mainly related to insufficient temperature control.

In fact, at temperatures above 650 ° C there are problems of the sublimation of metals, the formation of carbonyls and the agglomeration of metal oxides due to the formation of eutectics with low melting points; and thus, the incineration waste is in unsuitable form for the subsequent extraction of metals.

Multi hearth furnaces and rotary kilns have additional disadvantages, such as:

- phenomena of corrosion of the refractory due to the movement of the burnt product;

- non-uniform particle size of the resulting product due to uneven combustion;

- high fuel consumption for auxiliary burners and intense flow of combustible gas due to the low efficiency of the exchange between solid and gas / air.

Fluidized bed plants, in turn, have several drawbacks, mainly due to their complexity; and in order to prevent the formation of plugs, it is necessary to add an inert substance or limestone to the fluidized bed, which thus pollutes the resulting metal oxides.

Even subsequent leaching (for the separation of metals from oxides) has drawbacks, mainly due to the quality of the products leaving the waste incinerators of the mentioned type.

For example, in the case of vanadium recovery, the leaching of a mixture of metal oxides, which can be carried out using alkalis or acids, is problematic due to the properties of the solid substance leaving the waste incinerators and require a high consumption of chemicals; it is also sometimes necessary to go through various stages to separate vanadium from other metals. Ultimately, the extraction of vanadium from metal oxides present in refinery wastes presents various difficulties, including the large amount of carbon present in the oxides and the chemical and physical properties (in particular the presence of agglomerates), which can make leaching difficult and expensive.

Even greater difficulties arise in the case of the extraction of molybdenum, which is present in high concentrations, especially in the waste from processing using the thick suspension technology carried out with a catalyst (as, for example, in the aforementioned suspension technology EST-ENI), where molybdenum sulfides are used as catalysts ; various molybdenum compounds are in the sludge of these processes mixed with nickel and vanadium oxides; the amount of molybdenum can be in the same order as the amount of vanadium.

Molybdenum recovery is also carried out using leaching processes of a mixture of oxides carried out with alkalis or acids; however, in the case of molybdenum, its extraction is more complicated than in the case of extracting only vanadium, due to the fact that these two metals and their compounds have similar characteristics, so that their extraction and separation are difficult and require a large consumption of chemicals; in addition, multiple processing steps may be required to separate molybdenum from vanadium and other metals.

Extraction of molybdenum in this way presents problems similar to problems in the extraction of vanadium alone, such as the large amount of carbon present in the oxides, as well as the chemical and physical properties (presence of agglomerates), which can make leaching difficult and expensive. However, the presence of molybdenum makes the extraction and separation from vanadium more complicated, since leaching usually results in a solution containing vanadium and molybdenum compounds with similar characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus and method for extracting metals and metal oxides from industrial wastes, in particular oil refining waste products (oil refining waste), which would not have the aforementioned disadvantages of the prior art.

The present invention thus relates to a plant and method for recovering metals and / or metal oxides from industrial wastes, in particular petroleum refining waste products (oil refining waste), as defined in the characteristics in paragraph 1 and 14 of the attached claims.

Further preferred features of the present invention are provided in the dependent claims.

In accordance with the present invention, the extraction of metals from oil refinery waste or from other industrial waste is carried out using a conveyor furnace in which the controlled burning of processed waste (containing recoverable metals) takes place.

The use of a conveyor furnace in the process of extracting metals from industrial waste, in particular from oil refinery waste, provides several advantages over the prior art.

Firstly, the use of a conveyor furnace allows the burning of processed waste with precise temperature control, affecting the following parameters:

- the flow rate of solid waste fed into the furnace, thereby changing the thickness of the solid waste on the conveyor belt;

- the flow rate of combustion air, thus changing the speed of the gas phase in the furnace;

- the speed of the conveyor belt, thus changing the residence time of solid waste in the furnace.

The conveyor oven also allows local temperature control by using a series of burners for low temperature control (designed to raise the temperature if it is too low) and a series of air and / or water injectors for high temperature control (designed to reduce the temperature if it is too high), distributed along the longitudinal direction (length) of the furnace.

The use of a conveyor furnace in this case allows you to distribute the processed waste with a selected thickness, suitably reduced in order to limit the time spent in the furnace. Thus, the process in accordance with the present invention in comparison with other technologies requires a shorter technological time.

In addition to this, the conveyor furnace is easily and efficiently integrated with various devices complementary to the installation, in particular, such as a dryer, a chamber for burning light components, a pyrolysis unit and a filter unit for combustible gas.

In particular, the configuration of the conveyor furnace allows the filtration unit to be placed above the furnace so as to transfer (return) the dust captured by the filtration unit directly to the furnace.

The configuration of the conveyor furnace also makes it possible to simply and efficiently inject solid material containing possible metals onto the solid material containing recoverable metals, possible reagents, for example reagents that facilitate processing of the product in the subsequent stages of the extraction process, especially during leaching.

In one preferred embodiment of the present invention, a solution of sodium carbonate (Solve carbonate) is introduced into the furnace. Due to this, as well as due to the combustion of carbon, reactions between sodium carbonate and molybdenum and vanadium oxides occur in a controlled (temperature and residence time in an oxidizing environment) mode in the furnace, so as to capture SO ₂ and SO ₃ and form compounds useful for the subsequent stage of leaching (contributing to the extraction of metals, in particular their transition into solution).

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the present invention will become apparent from the description of the following non-limiting embodiments with reference to the attached drawings, in which:

- FIG. 1 is a schematic representation of a first embodiment of a plant for recovering metals and / or metal oxides or residues from industrial waste in accordance with the present invention;

- FIG. 2 is a schematic illustration of a second embodiment of an apparatus in accordance with the present invention;

- FIG. 3-6 are schematic views of further embodiments of the apparatus in accordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows in a schematic form an apparatus and method for extracting metals and / or metal oxides from industrial wastes, in particular wastes obtained from refining of petroleum products (refinery wastes).

For example, the waste treated in unit 1 is the ash obtained in gasification processes, which in particular contains nickel, vanadium and molybdenum oxides.

In the embodiment shown in FIG. 1, installation 1 makes it possible to extract a solid phase enriched with metals from industrial waste, mainly in the form of oxides; said oxides can then be sent to a subsequent metal separation step (described by way of example below).

The installation 1 mainly comprises a conveyor furnace 2, a pre-treatment unit 3 located in front of the conveyor furnace 2 along the path of the processed waste, and an exhaust gas treatment group 4 that receives and processes the exhaust gases generated in the conveyor furnace 2.

The conveyor furnace 2 comprises a housing 5 provided with an internal chamber 6 and extending along a longitudinal axis (essentially horizontal when used) between two opposite ends 7, 8; and a conveyor belt 9 located in the chamber 6 and extending along the axis A. The conveyor belt 9 is closed in a ring and has a substantially horizontal configuration, passing around at least two parallel end rollers 10 arranged orthogonally to axis A and essentially horizontally at the ends 7, 8 are furnaces that support and move the conveyor belt 9 (for simplicity, the drive system for rotating the rollers 10 is not shown).

Not necessarily, the conveyor belt 9 is also supported by additional intermediate rollers (not shown) located between the end rollers 10.

In the example shown in FIG. 1 (and in the following drawings), the conveyor belt 9 rotates clockwise, so that it has an upper surface 11 that receives the processed waste, transfers it along axis A to the chamber 6 and moves from end 7 to end 8.

The end 7 is provided with a main inlet 12 for supplying processed solid waste. The opposite end 8 is provided with a gas phase inlet 13 for supplying to the conveyor furnace 2 by means of a supply fan 14 mounted on the gas supply pipe 15 for combustion air; as well as a solid phase outlet 17 connected to an outlet line 18 from which solid matter is collected that has passed through a conveyor furnace 2 and which constitutes a metal-rich solid phase (mainly in the form of oxides).

The conveyor furnace 2 is also provided with an exhaust gas outlet 19 connected to the end 7, through which the exhaust gases generated in the chamber 6 are removed from the conveyor furnace 2 by means of an exhaust fan 20 installed on the exhaust gas discharge line 21.

Preferably, the conveyor furnace 2 is provided with a temperature control system 22 comprising a series of water or air cooling injectors 23 connected to a cooling or extinguishing line 24 and / or a series of burners 25 fed through a fuel line 26; the fuel pipe 26 and burners 25 are also used to initiate waste incineration in the initial phase of the conveyor furnace 2 and, if necessary, to support combustion during normal operation of the conveyor furnace 2.

If, as shown in FIG. 1, water is used to control the temperature in the conveyor furnace 2, the injectors 23 are water sprayers, and the line 24 is connected to the hydraulic circuit 27.

Injectors 23 and burners 25 are distributed along the longitudinal direction (length) of the conveyor furnace 2 and are thus spaced apart along axis A. The injectors 23 and burners 25 are controlled by a control unit (not shown) that acts on the injectors 23 and burners 25 so that locally regulate the temperature in the conveyor furnace 2, if necessary acting even differentially in different areas of the conveyor furnace 2.

The pre-treatment unit 3 is installed in front of the conveyor furnace 2 on the supply pipe 30, which delivers the processed waste to the installation 1; and serves mainly to reduce the water content (moisture) in the waste, which is then fed to the conveyor furnace 2, and is used in cases where the treated waste contains a significant amount of water, such as waste gasification processes, and therefore contains at least one solid-liquid separation device 28 or a dryer.

In the embodiment shown in FIG. 1, the pretreatment unit 3 contains in particular a centrifuge 28. As is known, the centrifuge performs the separation of components with different densities, in particular separating the solid phase from the liquid phase. Therefore, the centrifuge usually has a fixed part, a part rotating at high speed, and a spiral auger.

The centrifuge 28 has an inlet 29 connected to the supply pipe 30, which delivers the processed waste to the installation 1; and an outlet for solids and an outlet 32 for liquids located respectively on opposite axial ends of the centrifuge 28. The outlet for solids is connected via a supply pipe 33 to the main inlet 12 of the conveyor furnace 2; the fluid outlet 32 is connected to the hydraulic circuit 27 via a recirculation line 34 in order to reuse the water recovered in the pre-treatment unit 3. For example, the extracted water can be returned to the industrial plant with which unit 1 is associated (and from which it receives processed waste); and / or to the heat control line 24 of the conveyor furnace 2.

The flue gas treatment group 4 is located on the flue gas exhaust line 21 and processes the flue gases of the conveyor furnace 2 before being released to the atmosphere.

The exhaust gas treatment group 4 comprises, for example, a cooling unit 35 (heat exchanger, evaporator, etc.) and a filtering unit 36.

The filtration unit 36 contains in particular an electrostatic precipitator 37, which separates solid particles from the exhaust gases (essentially ash particles) that may be present in the exhaust gas. The electrostatic precipitator 37 has an exhaust gas inlet 38 connected to the exhaust gas outlet 19 by a first section 21a of the exhaust gas discharge line 21; an ash outlet 39 associated with a secondary inlet of the conveyor furnace 2 by means of a secondary supply pipe 41 for supplying ash extracted from the exhaust gases to the conveyor furnace 2; and an exhaust gas outlet 42 connected to the chimney 43.

An exhaust fan 20, which ensures the extraction of exhaust gases from the chamber 6 of the conveyor furnace 2 and their circulation in the exhaust gas exhaust line 21 and through the exhaust gas treatment group 4, is located on the exhaust gas exhaust line 21, for example after an electrostatic precipitator 37.

In use, the processed industrial waste, in particular oil refining waste (for example, coming from the gasification process), is first pre-treated in the pre-treatment unit 3, in particular in a centrifuge 28, to remove water.

The extracted water is returned to the hydraulic circuit 27. Solid waste in the form of granules, flakes or powder coming out of the pre-treatment unit 3 is fed into the conveyor furnace 2 from the end 7 through the inlet 12; this solid waste falls on the upper surface 11 of the conveyor belt 9 and is distributed along the entire width of the conveyor belt 9 (possibly by means of a feeding device moving across the conveyor belt 9).

While the belt conveyor 9 moves endlessly around the end rollers 10, solid waste is carried by the belt conveyor 9 along the chamber 6 (along the feed direction defined by axis A).

Dimensional (such as the length and width of the conveyor belt 9) and operating parameters (such as the speed of the conveyor belt 9 and the residence time of the waste in the conveyor furnace 2) can be selected as necessary.

For illustration purposes only, the conveyor belt 9 moves, for example, at a speed of the order of 1-2 m / min; conveyor furnace 2 has a length of 20-60 m; the waste residence time in the furnace is more than 10 minutes

The burning of solid waste (especially the carbon-containing component) takes place in a conveyor furnace 2.

At the time of starting the conveyor furnace 2, it may be necessary to initiate the burning of waste, for example by means of burners 25 fed by a fuel line 26; subsequently, after full access to the operating mode, the waste burning will become self-sustaining.

Combustion air and exhaust gases generated during the combustion of waste inside the chamber 6 flow countercurrent to the waste: while the waste moves (along with the conveyor belt 9) from end 7 to end 8, air and exhaust gases move in the opposite direction, from end 8 to end 7, where they exit through the exhaust gas outlet 19.

To eliminate dust settling in the lower part of the conveyor furnace 2, the conveyor belt 9 can be equipped with partitions located at intervals along the conveyor belt 9, which push the dust settling in the lower part of the conveyor furnace 2 to the end 7, where it can be collected and returned to conveyor belt 9.

In order to prevent leakage of exhaust gases from the conveyor furnace 2, the chamber 6 is maintained under a small vacuum by means of suitable balancing of the exhaust fan 20 and the supply fan 14.

In the area of the conveyor furnace 2, which is located at the end 7, near the inlet 12 through which the treated solid waste is fed, drying and burning of light waste components takes place; in the region which is located at the opposite end 8, near the outlet for the solid phase, the cooling of the waste in question is performed by the incoming air. As a result, at the ends 7, 8 of the conveyor furnace 2, the temperature may be lower than in its central region.

In the central region of the conveyor furnace 2, carbon-containing components of the waste are burned. In this area, temperature tends to increase. In order to prevent the agglomeration of solids through the formation of fusible eutectics and the sublimation of metals with the possible formation of carbonyls, the temperature should be kept below 650 ° C, preferably below 600 ° C.

As a result, the conveyor belt 9 is made of a material, in particular a metal material, having design temperatures of more than 650 ° C, namely, a material that is resistant to at least a temperature of 650 ° C.

Control of the average temperature in the Central region of the conveyor furnace 2 is achieved by influencing the following parameters:

- the flow rate of solids, thus changing the thickness of the layer on the conveyor belt 9;

- air flow rate, thereby changing the speed of the gas phase in the conveyor furnace 2;

- the speed of the conveyor belt, thereby changing the residence time of the solid substance inside the conveyor furnace 2.

Temperature control along the conveyor furnace 2 is achieved by a temperature control system 22 that controls the operation of the injectors 23 and / or burners 25.

Hot exhaust gases exit through the exhaust gas outlet 19 and are sent to the exhaust gas treatment group 4 before releasing them to the atmosphere.

Accordingly, in group 4 of the off-gas treatment, the off-gases are cooled to a temperature of 210 ° -350 ° C and filtered to remove dust. Using an electrostatic filter (precipitant) in the filtration unit 36, it is possible to process exhaust gases at temperatures up to 350 ° C; alternatively, a bag filter can be used, but in this case the exhaust gases should be cooled to temperatures of about 220 ° C (temperatures below 210 ° C should be avoided, because this tends to stick to dust and clog the bag filter).

The metal oxides contained in the solid phase leaving the conveyor furnace 2 are then processed to recover the metals, in particular by leaching and subsequent separation (for example, by precipitation and / or extraction).

In accordance with one aspect of the present invention illustrated in FIG. 2, the conveyor furnace 2 is equipped with a chemical distribution system 45 by which suitable chemicals can be introduced into the chamber 6 along the longitudinal direction of the conveyor furnace 2 and / or in predetermined areas of the chamber 6.

In particular, in order to facilitate the subsequent leaching stage, a chemical distribution system is used to inject into the mass of solid waste advancing in the conveyor furnace 2, a solution of sodium carbonate (Solve carbonate).

Sodium carbonate actually reacts in a conveyor furnace 2 with vanadium oxides, forming sodium metavanadate and sodium pyrovanadate, as well as with molybdenum oxides, forming sodium molybdenum.

In more detail, sodium carbonate reacts with molybdenum trioxide (MoO ₃ ) to form molybdenum sodium (Na ₂ MoO ₄ ); as well as with vanadium pentoxide (V ₂ O ₅ ), forming sodium metavanadate (NaVO ₃ ), and then pyrovanadate (Na ₄ V ₂ O ₇ ).

Typically, the reactions for the formation of sodium molybdenum acid and sodium metavanadate, shown below, occur simultaneously:

Na ₂ CO ₃ + MoO ₃ → Na ₂ MoO ₄ + CO ₂

Na ₂ CO ₃ + V ₂ O ₅ → 2 NaVO ₃ + CO ₂

Sodium molybdenum (Na ₂ MoO ₄ ) and sodium metavanadate (NaVO ₃ ) can be easily and effectively recovered as a solution using water leaching, as described below.

The chemical distribution system 45 comprises a series of nozzles 46 spaced along the axis A in the chamber 6 and connected to the chemical supply conduit 47. Nozzles 46 are preferably located above the upper surface 11 of the conveyor belt 9.

Injection of the sodium carbonate solution through nozzles 46 located at intervals along the conveyor furnace 2 allows precise control of the amount and distribution of sodium carbonate and thus the reactions of sodium carbonate with vanadium oxides and molybdenum oxides.

In addition, it is possible to vary the injection of the sodium carbonate solution along the A axis and along the length of the conveyor furnace 2 (i.e., to inject different amounts of solution in different areas of the conveyor furnace 2, at different positions along the A axis) depending on operating parameters such as temperature, speed conveyor belt, solids flow rate, gas phase (exhaust gas) flow rate to maximize the formation of sodium molybdenum acid and sodium metavanadate.

In the conveyor furnace 2, the injection of sodium carbonate solution does not entail corrosion problems, because the materials of the conveyor furnace 2, especially the material from which the conveyor belt 9 is made, are not corroded in the presence of sodium (as is the case with refractory materials used, for example, in multi-level rotary kilns that sodium attacks and damages in depth).

The solid product exiting the conveyor furnace 2 is sent to a recovery section 48 comprising in particular at least one leach unit 49, where water leaching takes place.

Leaching (or extraction of a solid with a liquid) consists of isolating one or more soluble components from the solid mass by means of a solvent.

In the process of the present invention, the solvent is water, and the solid phase entering the leach unit 49 is a mixture of mainly sodium molybdenum (Na ₂ MoO ₄ ) and sodium metavanadate (NaVO ₃ ), which are formed in the conveyor furnace 2 by injection of calcium carbonate as well as nickel oxide (NiO).

From leaching unit 49, a solution of sodium molybdenum acid (Na ₂ MoO ₄ ) and sodium metavanadate (NaVO ₃ ), as well as a solid substance containing primarily nickel oxide, are obtained.

The leach unit 49 has an inlet 51 connected by an outlet line 18 to an outlet 17 for a solid phase of the conveyor furnace 2 for supplying a solid phase to the leach unit 49; a water inlet 52 connected to a water supply line 53 to the leach unit 49; an upper outlet 54 from which an aqueous solution containing extracted metals, in particular vanadium and molybdenum, leaves; and a lower outlet 55, from which a solid phase exits containing oxides of nickel and other unrecovered metals.

Leaching is carried out, for example, at temperatures from 60 ° C to 100 ° C and a residence time of about 3 hours. To keep the solution warm, you can use the heat of the solid phase leaving the conveyor furnace 2, directing the solid phase leaving the furnace (at temperatures above 100 ° C) directly to the leaching unit 49.

After water leaching, most of the molybdenum and vanadium are in the solution in the form of sodium metavanadate and sodium molybdenum acid, while nickel and other metal oxides are in the solid phase with a higher concentration than in the solid that is included in the leaching unit 49.

The solid phase containing nickel oxide and leaving the leach unit 49 can be sent to the conveyor furnace 2 through a drying line 56, which leaves the lower outlet 55 of the leach unit 49, for drying in the section of the conveyor furnace 2, as shown schematically in FIG. 2.

Since the concentration of nickel in the solid phase after leaching is much higher than the normal concentration in minerals mined in mines, the solid product exiting unit 1 is suitable for extraction or extraction of nickel.

The injection of the sodium carbonate solution into the conveyor furnace 2 to increase the subsequent extraction of vanadium and molybdenum in the leach unit may be higher than the stoichiometric amount, in which case the excess will pass into the liquid solution leaving the leach unit 49. If there is a large excess of sodium carbonate, part of the solution can be returned to the conveyor furnace 2.

A solution of sodium molybdenum acid (Na ₂ MoO ₄ ) and sodium metavanadate (NaVO ₃ ) can be used in various processes to extract molybdenum and vanadium (extract vanadium and molybdenum in quantities of over 80% and even more than 90% of their initial content in waste processed in this installation), such as:

1. fractional precipitation of ammonium molybdenum acid and ammonium metavanadate;

2. fractional precipitation of molybdenum and molybdenum disulfide (MoS ₃ ) using H ₂ S;

3. fractional precipitation of sodium metavanadate (NaVO ₃ ) by adding ammonium salts and extraction with a solvent, for example containing amino groups.

These processes can be easily performed in place, after the leaching stage, that is, on the same installation 1.

FIG. 3 schematically shows one preferred embodiment for recovering molybdenum and vanadium after leaching.

As described previously, in the conveyor furnace 2, sodium molybdenum and sodium metavanadate are formed by the injection of sodium carbonate through the chemical distribution system 45. The solid phase leaving the conveyor furnace 2 and containing sodium molybdenum acid and sodium metavanadate is sent to the recovery section 48.

The extraction section 48 includes a leaching unit 49, where sodium molybdenum and sodium metavanadate are transferred to the solution, as well as one or more metal separation units 57, 58, where the vanadium and molybdenum are separated and recovered.

In particular, a solution of sodium molybdenum acid and sodium metavanadate exiting the leaching unit 49 is first sent through a first connecting line 61, which leaves from the upper outlet 54, to a vanadium deposition unit 57 into which ammonium sulfate is supplied via a supply line 62, and where vanadium is recovered by precipitation of ammonium metavanadate with ammonium sulfate in an alkaline medium (at pH greater than 8).

The reaction for the fractional precipitation of ammonium metavanadate at alkaline pH is as follows:

2 NaVO _{3 solution} + (NH ₄ ) ₂ SO ₄ → 2NH ₄ VO _{3 precipitate} + Na ₂ SO _{4 solution}

From the vanadium deposition unit 57, an ammonium metavanadate precipitate is obtained, which is discharged from the lower outlet 63 of the unit 57; and also a solution containing a reduced amount of ammonium molybdenum acid and ammonium metavanadate.

This solution is routed through a second connecting line 64 to a molybdenum precipitation or extraction unit 58 to extract molybdenum. The step of extracting molybdenum from the solution can be performed using various known processes, such as:

- fractional precipitation of ammonium molybdenum acid by changing the acidity of the solution (for example, using sulfuric acid to an acidic pH of about 1-2) using ammonium salts (such as ammonium sulfate), in accordance with the reaction:

Na ₂ MoO _{4 solution} + (NH ₄ ) ₂ SO ₄ → (NH ₄ ) ₂ MoO _{4 precipitate +} Na ₂ SO _{4 solution}

- fractional precipitation of molybdenum disulfide (MoS ₃ ) formed during the reaction of molybdate with hydrogen sulfide (H ₂ S), in accordance with the reaction:

H ₂ MoO _{4 solution} + 3H ₂ S _gas → MoS _{3 precipitate +} 4 H ₂ O;

- liquid extraction using solvents containing, for example, amino groups (trioctyl / dodecylamine, Alamine 336; tri-n-octylamine, TOA; tri-n-dodecylamine, Alamine 304, quaternary ammonium salts) or others, such as hydroxydecane-7- 6-diethyl-5.8-oxime (LIX 63).

In the embodiment depicted in FIG. 3, for example, the molybdenum precipitation unit 58 is fed through the respective reactant supply lines 65, 66 with ammonium sulfate and sulfuric acid, and produces a precipitate of ammonium molybdenum acid.

This ammonium molybdenum acid precipitate is routed through a connecting line 67 to a saponification unit 68, where it is treated with organic carboxylic acids supplied through an acid supply line 69 to form molybdenum soap.

Commonly used acids are naphthenic acids; oxalic acids can be used as an accelerator of the saponification reaction; saponification is carried out presumably at temperatures of about 100 ° -300 ° C, preferably 200-250 ° C, for about 5-12 hours.

Molybdenum soap is obtained by saponification (usually Mo naphthenate) with a softening point of about 120 ° C and a molybdenum content of 4-7%, preferably 6%.

The soap obtained, discharged from the outlet 70, is suitable for use in hydroconversion by-product purification processes using suspension technology using catalysts, with molybdenum disulfide (MoS ₂ ) being used as a catalyst precursor. This soap is actually soluble in the charge used in these processes, forming a homogeneous solution of molybdenum; inside the reactors used in this technology, molybdenum reacts with H ₂ S and hydrogen to form molybdenum sulfide (MoS ₂ ), which acts as a catalyst.

Unit 1 and the process described above implemented in it can be modified in various ways, including depending on the type of industrial waste processed.

For example, pretreatment unit 3 may be unnecessary if the waste being processed is sufficiently dry.

The pre-treatment unit 3 may include, instead of the centrifuge described above, a device for separating various types of solids and liquids, or a dryer.

For example, in the embodiment shown in FIG. 4 for treating gasification waste, the pre-treatment unit 3 includes a dryer 74, in particular a cyclone dryer.

The cyclone dryer 74 also provides direct discharge of the dried product to the conveyor belt 9 of the conveyor furnace 2; in addition, it is possible to use part of the hot exhaust gases leaving the conveyor furnace 2 in a cyclone dryer 74, reducing the use of fuel required for drying.

Therefore, the dryer 74 has an inlet 75 connected to a supply pipe 30 that delivers the waste to be processed into the installation 1; an outlet for solids connected through an inlet pipe 33 to an inlet 12 of the conveyor furnace 2; an exhaust gas inlet 78 connected to an exhaust gas outlet 19 of the conveyor furnace 2 by a first section 21a of the exhaust gas exhaust line 21; a gas outlet 79 connected to a second part 21b of the exhaust gas discharge line 21 and thus to the exhaust gas treatment group 4.

The gases leaving the dryer 74 are then sent to the off-gas treatment group 4, where they are filtered along with the off-gases coming from the conveyor furnace 2.

It is understood that the apparatus 1 shown in FIG. 4 may also include a chemical distribution system 45 and an extraction section 48 (not shown in FIG. 4).

FIG. 5 illustrates one embodiment, particularly suitable for treating wastes containing a substantial amount of light hydrocarbons, such as wastes from hydroconversion processes using slurry technology for treating heavy oil refinery (slurry technology type EST from ENI).

In this embodiment, the pre-treatment unit 3 includes a combustion chamber 80, in particular a cyclone combustion chamber, which is fed by the treated waste.

Thus, the combustion chamber 80 has an inlet 81 connected to the supply pipe 30, which transfers the processed waste to the installation 1; combustion air inlet 82; an inlet 83 for optionally introducing steam and / or water; an outlet 84 for particulate matter connected through an inlet pipe 33 to an inlet 12 of a conveyor furnace 2 for unloading onto the conveyor belt 9 dust generated in the combustion chamber 80; a service inlet 85 associated with a chemical distribution system 45 (in particular through a branch of the chemical supply line 47) for introducing chemicals into the waste to be treated already in the pre-treatment unit 3; an exhaust gas outlet 86 connected to an exhaust gas discharge line 21 and thus to an exhaust gas treatment group 4.

The temperature in the combustion chamber 80 can be controlled both by controlling the air flow entering the combustion chamber 80, and by controlling the flow of steam and water.

The flue gases leaving the combustion chamber 80 can be treated in the flue gas treatment group 4 for cleaning along with the flue gases coming from the conveyor furnace 2 using the same filtering unit 36.

In case it is desirable to recover the heat generated in the combustion chamber 80, as well as the heat of the exhaust gases coming from the conveyor furnace 2, the exhaust gas treatment group 4 may include one evaporator 87, which constitutes the cooling unit 35 and is placed in front of the filtration unit 36 in order to ensure heat recovery of exhaust gases coming from both the combustion chamber 80 and the conveyor furnace 2.

Injecting chemicals is particularly advantageous when the waste being processed contains a significant amount of sulfur, and it is desirable to reduce the amount of sulfur compounds.

By injecting sodium carbonate using the chemical distribution system 45 directly into the pre-treatment unit 3 and / or into the conveyor furnace 2, the SO ₂ / SO ₃ content can be reduced. Reactions of sodium carbonate with sulfur compounds give sodium sulfates / sulfites and possibly salts mixed with vanadium, which is in the form of oxides leaving the conveyor furnace 2. Such products facilitate the leaching of vanadium and molybdenum, so the presence of sulfur in the process in accordance with the present invention brings benefits, while in the most widely used processes of the prior art, the presence of sulfur is usually a problem.

FIG. 6 illustrates one embodiment, shown particularly for treating waste from a combustion process, or system, such as petroleum coke burning ash or petroleum waste.

In this case, the waste processed in unit 1 consists of ash discharged from the evaporator 88, where petroleum coke and / or oil refinery waste is burned.

The exhaust gas treatment group 4 is integrated into the exhaust gas ventilation-filtration-purification system 89 coming from the evaporator 88 and essentially comprises a filter 90, in particular an electrostatic filter, one or more fans 91 and a purification device 92, in particular an exhaust gas desulfurization device (FGD).

The ash after combustion from the evaporator 88 is sent to the conveyor furnace 2 through the inlet pipe 33 and the inlet 12; the exhaust gases generated in the evaporator 88 are directed to a filter 90 connected to the evaporator 88 by the exhaust gas line 93, which also connects the exhaust gas exhaust line 21 from the conveyor furnace 2; the filter 90 thus processes both the off-gases of the evaporator 88 and the off-gases of the conveyor furnace 2 mixed together; the ash recovered from the filter 90 is returned to the conveyor furnace 2 through a recirculation line 94 connected to the inlet pipe 33, and thus combined with the ash coming directly from the evaporator 88; the exhaust gases leaving the filter 90 are sent to the purification device 92, and then released into the atmosphere from the chimney 43.

Finally, it is understood that numerous modifications and variations can be made in the described and illustrated installation and process, while remaining within the scope of the appended claims.

Claims (44)

1. Installation (1) for the extraction of metals from waste oil refining containing conveyor oven (2); a supply line (33) connected to the main inlet (12) of the furnace for feeding the furnace with solid waste containing metals, in particular in oxide form; an output line (18) associated with an outlet (17) of the solid phase furnace for recovering the metal-rich solid phase from the furnace, moreover the conveyor furnace (2) comprises an inner chamber (6) extending along a substantially horizontal longitudinal axis (A), as well as a closed belt conveyor (9) located in the chamber (6), having a substantially horizontal configuration along axis (A), and also having an upper surface (11) that receives the processed waste and transfers this waste along the axis (A) in the chamber (6) between the two longitudinally opposite ends (7, 8) of the conveyor furnace (2), respectively equipped with a main inlet (12) and an outlet (17) for the solid phase, characterized in that the installation comprises a leaching unit (49) installed after the conveyor furnace (2) and connected to the outlet (17) for the solid phase of the conveyor furnace (2), for leaching the solid phase exiting the conveyor furnace (2) and producing an aqueous solution containing metals recovered from said solid phase, moreover, one or more metal separation units (57, 58) are provided located after the leach unit (49) for at least partially separating the metals contained in the solution exiting the leach unit (49). 2. Installation according to claim 1, in which the first end (7) of the conveyor furnace (2), equipped with a main inlet (12), is also provided with an outlet (19) for the exhaust gas associated with the exhaust gas outlet line (21), equipped with an exhaust fan (20); and the second end (8) of the conveyor furnace (2), provided with an outlet (17) for the solid phase, is also provided with an inlet (13) for the gas phase connected to the gas supply line (15) equipped with a supply fan (14) for supplying combustion air into a conveyor oven (2). 3. Installation according to claim 1, in which the conveyor furnace (2) is equipped with a temperature control system (22) containing a series of injectors (23) of cooling water or air and / or a series of burners (25) located at a distance from each other along the axis (A). 4. Installation according to claim 1, containing a pre-treatment unit (3) installed in front of the conveyor furnace (2) along the waste route to reduce the water content in the waste, which is then fed to the conveyor furnace (2). 5. Installation according to claim 4, in which the pre-treatment unit (3) comprises a solid-liquid separation device (28) or a dryer. 6. Installation according to claim 4, in which the pre-treatment unit (3) comprises a centrifuge (28) having an inlet (29) connected to the supply pipe (30), which delivers the processed waste to the installation (1); and an outlet (31) for solids and an outlet (32) for liquids located at the respective axial ends of the centrifuge (28) and connected to the main inlet (12) of the conveyor furnace (2) and to the recirculation line (34), respectively. 7. Installation according to claim 1, containing an exhaust gas treatment group (4) connected to an exhaust gas outlet (19) for a conveyor furnace (2) for receiving and treating exhaust gas generated in a conveyor furnace (2). 8. Installation according to claim 7, in which the group (4) of the exhaust gas treatment comprises a filter unit (36), including in particular an electrostatic precipitator or filter (37). 9. Installation according to claim 7, in which the group (4) of the exhaust gas treatment comprises a cooling unit (35) located in front of the filter unit (36). 10. Installation according to claim 1, in which the conveyor belt (9) is made of a material, in particular a metal material, resistant to a temperature of at least 650 ° C. 11. Installation according to claim 1, in which the conveyor furnace (2) is equipped with a chemical distribution system (45) containing a series of nozzles (46) located at a distance from each other along the axis (A) in the chamber (6) and connected to the pipeline (47) supplying chemicals to spray chemicals, in particular sodium carbonate solution, into the chamber (6) and / or to solid waste lying on the conveyor belt (9) along the axis (A) and / or in the predetermined zones of the chamber (6) . 12. A method of extracting metals from waste oil refining, including a burning step in which solid waste is burned to reduce the carbon content of said waste and to produce a metal-enriched solid phase; a recovery step in which metals are recovered from said metal-rich solid phase, characterized in that the combustion stage contains: a waste distribution step on the upper surface (11) of the closed belt conveyor (9) having a substantially horizontal configuration along axis (A), the step of advancing the conveyor belt (9) along the axis (A) and thereby moving the waste lying on the conveyor belt (9) along the direction of advancement defined by the axis (A), while supplying heat to the waste in order to cause the waste to burn, the stage of removal from the surface (11) of the conveyor belt (9) of the solid phase enriched with metals, while the extraction stage contains: the stage of leaching with water of a solid phase removed from the conveyor belt (9), obtaining a solution and a metal separation step for separating, at least in part, the metals contained in the solution obtained in the leaching step. 13. The method according to p. 12, which includes the stage of supplying combustion air and, if necessary, combustible gas to facilitate the combustion of waste and the removal of exhaust gas generated by the combustion of waste; while the combustion air and the exhaust gas move countercurrently relative to the direction of movement of the waste. 14. The method according to p. 12, comprising the step of adjusting the temperature at the stage of combustion through a series of injectors (23) of cooling water or air and / or a series of burners (25) located at a distance from each other along the axis (A). 15. The method according to p. 12, including the stage of pre-treatment of waste, in which water is removed from the waste before the stage of burning to reduce the water content in the waste, which is then fed to the stage of burning. 16. The method according to p. 15, in which the stage of pre-treatment of waste includes the stage of separation of solids and liquids or stage drying. 17. The method according to p. 15, in which the stage of pre-treatment of waste is carried out by means of a centrifuge (28). 18. The method according to p. 12, comprising the stage of processing the exhaust gas, which carry out the filtering of the exhaust gas generated in the combustion stage. 19. The method according to p. 18, in which the exhaust gas is filtered by means of an electrostatic precipitator or filter (37). 20. The method according to p. 18, in which the stage of processing the exhaust gas includes the step of cooling the exhaust gas before filtering it. 21. The method according to p. 12, in which the conveyor belt (9) is made of a material, in particular a metal material, resistant to a temperature of at least 650 ° C. 22. The method according to p. 12, containing the stage of distribution of chemicals, in which one or more chemicals are sprayed in the chamber (6) and / or on solid waste lying on the conveyor belt (9), along axis (A) and / or in predetermined areas of the chamber (6), through a series of nozzles (46) located at a distance from each other along the axis (A). 23. The method according to p. 22, in which a solution of sodium carbonate is injected in order to form the sodium salts of the metals contained in the waste. 24. The method according to p. 23, in which the processed waste contains Mo and Va, as well as Ni, mainly in oxide form; and the injection of sodium carbonate leads to the formation of sodium molybdenum (Na ₂ MoO ₄ ) and sodium metavanadate (NaVO ₃ ). 25. The method according to p. 24, in which at the stage of water leaching of the solid phase removed from the conveyor belt (9), a solution of sodium molybdenum acid (Na ₂ MoO ₄ ) and sodium metavanadate (NaVO ₃ ), as well as a solid substance containing oxide nickel. 26. The method according to p. 25, in which at the stage of separation of metals to separate, at least partially, the metals contained in the solution obtained at the stage of leaching, vanadium and molybdenum are separated.

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